The primary aims of this grant are to clarify the role played by dentin phosphoprotein (DPP) in the remineralization (and mineralization) Of human dentin; and identify that there may be differences in root versus crown DPP. It is proposed that both the quantity and quality, as defined by protein sequence, molecular weight, amino acid and immunoreactivity, affect the mineral composition, crystal orientation and mineral distribution in remineralized (repaired) dentin. It is further hypothesized that this repaired tissue will exhibit certain relevant clinical characteristics; be less susceptible to demineralization; be amenable to the bonding of restorations, and be physiologically functional. Sequential extracts and digests of human dentin will be analyzed to establish their DPP composition. Then the effects that the different "pools" of DPP; molecular species, degraded versus non-degraded, extractable (soluble) versus non-extractable (insoluble), which remain in dentin after these extractions, will have on the remineralization potential of the dentin, the mineral characteristics and the mechanical properties of the repaired tissue will be assessed. The demineralized and extracted matrices will be remineralized using an artificial solution with chemical characteristics similar to that of serum (mineralization). Clarified saliva (remineralization) will also be used to try and estimate the effects of the salivary proteins on the process. The remineralization will take place at 37 degrees C at near neutral pH, and extend for a period of three weeks, or until remineralization is "complete". The remineralized tissue will be characterized using x-ray diffraction, SEM, TEM and microradiography and the mechanical properties analyzed by bulk compression tests and local hardness and stiffness using atomic force microscopy. The ability of the tissue to withstand demineralization (caries) will be tested in an in vitro caries system and compared with normal dentin. The dentin specimens will be analyzed using quantitative microradiography. The observations will be the first to compare the quantity and quality of DPP in human coronal, versus root dentin. It will also relate the mineral characteristics of the remineralized human dentin to the various "pools" of highly purified and characterized DPP. Of equal importance to these basic science findings will be the clinical implications of the remineralization process which may ameliorate the significant and costly conditions, secondary, recurrent and root caries. Ultimately, once the DPP's and their activity (for example, initiating or blocking mineral formation) have been identified they can be used in optimizing the repair of diseased and/or compromised dental hard tissues.